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Visual FoxPro Examples

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(Visual FoxPro) Encrypting/decrypting a data stream.

This example demonstrates how to encrypt (using a symmetric encryption algorithm such as AES, ChaCha20, Blowfish, RC2, 3DES, etc) a large amount of data. The data is passed in chunks to one of the encrypt methods: EncryptBytes, EncryptString, EncryptBytesENC, or EncryptStringENC, etc. The FirstChunk and LastChunk properties are used to indicate whether a chunk is the first, middle, or last in a stream to be encrypted. By default, both FirstChunk and LastChunk equal 1 -- meaning that the data passed is the entire amount.

Note: You may feed the data in chunks that are smaller than the block size of the encryption algorithm (AES and Twofish have a block size of 16 bytes. DES, 3DES, Blowfish, and RC2 have a block size of 8 bytes. ARC4 and ChaCha20 are streaming encryption algorithms and don't have a block size, but technically you can think of it as having a block size of 1 byte.)

Chilkat will buffer the data as required. If an amount of data smaller than the block size is passed such that the entire amount is buffered, then an empty string (or 0 bytes) is returned. The buffered data will be added to the data passed in subsequent calls. When the final data chunk is passed, it is padded to the encryption algorithm's block size (according to the PaddingScheme property) and the encryption is complete.

Decrypting in chunks is identical to encrypting in chunks.

Chilkat ActiveX Downloads

ActiveX for 32-bit and 64-bit Windows

LOCAL loCrypt
LOCAL lcTxt1
LOCAL lcTxt2
LOCAL lcTxt3
LOCAL loSbEncrypted
LOCAL i
LOCAL lcDecryptedText

* This example requires the Chilkat API to have been previously unlocked.
* See Global Unlock Sample for sample code.

loCrypt = CreateObject('Chilkat_9_5_0.Crypt2')

loCrypt.CryptAlgorithm = "aes"
loCrypt.CipherMode = "cbc"
loCrypt.KeyLength = 128

loCrypt.SetEncodedKey("000102030405060708090A0B0C0D0E0F","hex")
loCrypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex")

loCrypt.EncodingMode = "hex"
lcTxt1 = "The quick brown fox jumped over the lazy dog." + CHR(13) + CHR(10)
lcTxt2 = "-" + CHR(13) + CHR(10)
lcTxt3 = "Done." + CHR(13) + CHR(10)

loSbEncrypted = CreateObject('Chilkat_9_5_0.StringBuilder')

* Encrypt the 1st chunk:
* (don't worry about feeding the data to the encryptor in 
* exact multiples of the encryption algorithm's block size.
* Chilkat will buffer the data.)
loCrypt.FirstChunk = 1
loCrypt.LastChunk = 0
loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt1))

* Encrypt the 2nd chunk
loCrypt.FirstChunk = 0
loCrypt.LastChunk = 0
loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt2))

* Now encrypt N more chunks...
* Remember -- we're doing this in CBC mode, so each call
* to the encrypt method depends on the state from previous
* calls...
loCrypt.FirstChunk = 0
loCrypt.LastChunk = 0

FOR i = 0 TO 4
    loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt1))
    loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt2))
NEXT

* Now encrypt the last chunk:
loCrypt.FirstChunk = 0
loCrypt.LastChunk = 1
loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt3))

? loSbEncrypted.GetAsString()

* Now decrypt in one call.
* (The data we're decrypting is both the first AND last chunk.)  
loCrypt.FirstChunk = 1
loCrypt.LastChunk = 1
lcDecryptedText = loCrypt.DecryptStringENC(loSbEncrypted.GetAsString())

? lcDecryptedText

* Note: You may decrypt in N chunks by setting the FirstChunk
* and LastChunk properties prior to calling the Decrypt* methods

RELEASE loCrypt
RELEASE loSbEncrypted


 

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